Questions: A mixture of gaseous reactants is put into a cylinder, where a chemical reaction turns them into gaseous products. The cylinder has a piston that moves in or out, as necessary, to keep a constant pressure on the mixture of 1 atm. The cylinder is also submerged in a large insulated water bath. From previous experiments, this chemical reaction is known to release 190 kJ of energy. The position of the piston is monitored, and it is determined from this data that the system does 153 kJ of work on the piston during the reaction. Is the reaction exothermic or endothermic? - exothermic - endothermic Does the temperature of the water bath go up or down? - up - down - neither Does the piston move in or out? - in - out - neither Does heat flow into or out of the gas mixture? - in - out - neither How much heat flows? Round your answer to 2 significant digits. - [ ] kJ

A mixture of gaseous reactants is put into a cylinder, where a chemical reaction turns them into gaseous products. The cylinder has a piston that moves in or out, as necessary, to keep a constant pressure on the mixture of 1 atm. The cylinder is also submerged in a large insulated water bath. From previous experiments, this chemical reaction is known to release 190 kJ of energy. The position of the piston is monitored, and it is determined from this data that the system does 153 kJ of work on the piston during the reaction. Is the reaction exothermic or endothermic? - exothermic - endothermic Does the temperature of the water bath go up or down? - up - down - neither Does the piston move in or out? - in - out - neither Does heat flow into or out of the gas mixture? - in - out - neither How much heat flows? Round your answer to 2 significant digits. - [ ] kJ
Transcript text: A mixture of gaseous reactants is put into a cylinder, where a chemical reaction turns them into gaseous products. The cylinder has a piston that moves in or out, as necessary, to keep a constant pressure on the mixture of 1 atm . The cylinder is also submerged in a large insulated water bath. From previous experiments, this chemical reaction is known to release 190. kJ of energy. The position of the piston is monitored, and it is determined from this data that the system does $153 . \mathrm{kJ}$ of work on the piston during the reaction. \begin{tabular}{|c|c|} \hline Is the reaction exothermic or endothermic? & \begin{tabular}{l} exothermic \\ endothermic \end{tabular} \\ \hline \begin{tabular}{l} Does the temperature of the water bath go up or \\ down? \end{tabular} & \begin{tabular}{l} up \\ down \\ neither \end{tabular} \\ \hline Does the piston move in or out? & \begin{tabular}{l} in \\ out \\ neither \end{tabular} \\ \hline Does heat flow into or out of the gas mixture? & \begin{tabular}{l} in \\ out \\ neither \end{tabular} \\ \hline \begin{tabular}{l} How much heat flows? Round your answer to 2 \\ significant digits. \end{tabular} & $\square \mathrm{kJ}$ \\ \hline \end{tabular}
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Solution

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Solution Steps

Step 1: Determine if the Reaction is Exothermic or Endothermic

A reaction is exothermic if it releases energy to the surroundings. In this case, the reaction is known to release 190 kJ of energy. Therefore, the reaction is exothermic.

Step 2: Determine the Temperature Change of the Water Bath

Since the reaction is exothermic, it releases heat to the surroundings. The water bath, being part of the surroundings, will absorb this heat, causing its temperature to go up.

Step 3: Determine the Movement of the Piston

The system does 153 kJ of work on the piston. When work is done by the system on the surroundings, it typically involves expansion, meaning the piston moves out.

Step 4: Determine the Direction of Heat Flow

In an exothermic reaction, heat flows out of the system. Therefore, heat flows out of the gas mixture.

Step 5: Calculate the Amount of Heat Flow

Using the first law of thermodynamics, which states that the change in internal energy (\(\Delta U\)) is equal to the heat added to the system (\(q\)) minus the work done by the system (\(w\)), we have: \[ \Delta U = q - w \] Given that the reaction releases 190 kJ of energy, this is the change in internal energy (\(\Delta U = -190 \, \text{kJ}\)), and the work done by the system is 153 kJ (\(w = 153 \, \text{kJ}\)), we can solve for \(q\): \[ -190 = q - 153 \] \[ q = -190 + 153 = -37 \, \text{kJ} \] The negative sign indicates that 37 kJ of heat flows out of the system.

Final Answer

  • The reaction is \(\boxed{\text{exothermic}}\).
  • The temperature of the water bath goes \(\boxed{\text{up}}\).
  • The piston moves \(\boxed{\text{out}}\).
  • Heat flows \(\boxed{\text{out}}\) of the gas mixture.
  • The amount of heat that flows is \(\boxed{37 \, \text{kJ}}\).
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